Design method of short duration cam, short duration cam, variable valve lift apparatus including the same, and design method of cam

ABSTRACT

A short duration cam of a variable valve lift apparatus has a cam lift acceleration including a first peak formed before a center of the cam lift acceleration, and a second peak formed after the center of the cam lift acceleration. A relative ratio of a smaller value to a greater value of the first peak and the second peak is 0.8 or more.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority to Korean Patent Application No. 10-2014-0067628 filed in the Korean Intellectual Property Office on Jun. 3, 2014, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a method for manufacturing a short duration cam, a short duration cam, a variable valve lift apparatus including the short duration cam, and a method for manufacturing a cam for relatively increasing a valve lift value.

BACKGROUND

Researches have been actively conducted into engine downsizing technologies, in particular, a downsizing technology of a gasoline direct injection (GDI) engine and a turbo gasoline direct injection (T-GDI) engine in a gasoline engine field in order to reduce fuel consumption and environment problems.

A miller cycle engine for enhancing a compression ratio and for early closing timing of an intake valve to improve fuel consumption of a downsizing engine has been introduced.

The Miller cycle engine has a relatively low compression ratio compared with a conventional internal combustion engine, has no knocking problem, and has a higher expansion ratio, thereby increasing engine efficiency.

FIG. 1 is a graph illustrating a general valve profile, and FIGS. 2( a) and 2(b) are graphs illustrating lift curves of a general cam.

For example, in the Miller cycle, opening and closing time of an intake valve needs to be adjusted or valve duration of the intake valve needs to be reduced. As shown in FIG. 1, valve lift of a cam C2 formed by simply reducing valve duration of a cam C1 having a general cam profile is reduced for example, from 8.5 mm to 6.5 mm.

As shown in FIG. 2( a), the general cam is designed in such a way that right and left portions of a valve lift acceleration are almost symmetrical with respect to each other based on a center thereof, and a cam lift acceleration is calculated from the valve lift acceleration.

In FIG. 2( b), right and left portions of the calculated cam lift acceleration are asymmetrical with respect to each other due to valve train structure characteristics. Here, a peak value B1 on the left is greater than a peak value B2 on the right, which affects a cam shape.

The horizontal axis represents a cam duration angle, and the vertical axis represents a cam lift in FIGS. 2( a) and 2(b).

That is, a curvature radius r1 of a concave portion of FIG. 5 is reduced.

When the curvature radius r1 is reduced, it is difficult to correspond to a grinding wheel for processing a concave shape, and thus, the curvature radius r1 needs to be increased.

However, in order to increase the curvature radius, a maximum cam acceleration value needs to be reduced. Accordingly, a maximum cam lift amount is reduced, and thus, a maximum valve lift amount is also reduced.

That is, as shown in FIG. 1, when the valve duration is reduced, a maximum opening amount of the valve lift is proportionally reduced, for example, from 8.5 mm to 6.5 mm.

The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure, and therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.

SUMMARY

The present disclosure has been made in an effort to provide a short duration cam and a variable valve lift apparatus including the same.

According to an exemplary embodiment of the present inventive concept, a method for manufacturing a short duration cam of a variable valve lift apparatus includes setting a cam lift acceleration of the short duration cam such that a first peak is formed before a center of the cam lift acceleration and a second peak is formed after the center of the cam lift acceleration. A curvature radius of a concave portion of the short duration cam is set based on the set cam lift such that a relative ratio of a smaller value to a greater value of the first peak and the second peak is 0.8 or more.

The short duration cam may have a duration angle of 100 to 120 degrees between opening and closing of a valve including a ramp of the short duration cam.

The short duration cam may have a valve lift profile to be asymmetrical based on a maximum valve lift of the short duration cam.

A short duration cam according to an exemplary embodiment of the present inventive concept may be applied to a short duration cam applied to a variable valve lift apparatus.

According to another embodiment of the present inventive concept, a short duration cam of a variable valve lift apparatus, wherein a cam lift acceleration of the short duration cam has a first peak formed before a center of the cam lift acceleration and a second peak formed after the center of the cam lift acceleration, and a relative ratio of a smaller value to a greater value of the first peak and the second peak may be 0.8 or more.

The short duration cam may have a duration angle 100 to 120 degrees between opening and closing of a valve including a ramp of the short duration cam.

The short duration cam may have a valve lift profile to be asymmetrical based on maximum valve lift of the short duration cam.

A variable valve lift apparatus according to an exemplary embodiment of the present inventive concept may include the short duration cam and a long duration cam.

The short duration cam may be closed before reaching a bottom dead center.

Yet according to another embodiment of the present inventive concept, a method for manufacturing a cam includes setting a cam lift acceleration of the cam such that a first peak is formed before a center of the cam lift acceleration and a second peak is formed after the center of the cam lift acceleration. A curvature radius of a concave portion of the cam is set based on the set cam lift such that a relative ratio of a smaller value to a greater value of the first peak and the second peak is 0.8 or more.

The cam may have a duration angle of 100 to 120 degrees between opening and closing of a valve including a ramp of the cam.

The cam may have a valve lift profile to be asymmetrical based on maximum valve lift of the cam.

According to a method for manufacturing a short duration cam, a short duration cam, a variable valve lift apparatus including the short duration cam and a method for manufacturing a cam according to exemplary embodiments of the present inventive concept, a valve lift value may be relatively increased, thereby increasing intake efficiency.

According to a method for manufacturing of a short duration cam, a short duration cam, a variable valve lift apparatus including the short duration cam, and a method for manufacturing a cam according to exemplary embodiments of the present inventive concept, a valve lift value may be relatively increased and thus the cam may be applied to Miller cycle engine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph illustrating a general valve profile.

FIGS. 2( a) and 2(b) are a set of graphs illustrating lift curves of a general cam.

FIG. 3 is a perspective view of a variable valve lift apparatus according to an exemplary embodiment of the present inventive concept.

FIGS. 4( a) and 4(b) are a set of graphs illustrating lift curves of a short duration cam of a variable valve lift apparatus according to an exemplary embodiment of the present inventive concept.

FIG. 5 is a diagram illustrating a general cam and a short duration cam of a variable valve lift apparatus according to an exemplary embodiment of the present inventive concept.

FIG. 6 is a graph illustrating valve profiles of a general cam and a short duration cam of a variable valve lift apparatus according to an exemplary embodiment of the present inventive concept.

DETAILED DESCRIPTION

In the following detailed description, only certain exemplary embodiments of the present inventive concept have been shown and described, simply by way of illustration.

As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present disclosure.

Throughout this specification, like reference numerals in the drawings denote like elements.

Throughout this specification, unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising” will be understood to imply the inclusion of stated elements but not the exclusion of any other elements.

An exemplary embodiment of the present inventive concept will hereinafter be described in detail with reference to the accompanying drawings.

FIG. 3 is a perspective view of a variable valve lift apparatus according to an exemplary embodiment of the present inventive concept, and FIGS. 4( a) and 4(b) are a set of graphs illustrating lift curves of a short duration cam of a variable valve lift apparatus according to an exemplary embodiment of the present inventive concept.

A short duration cam according to an exemplary embodiment of the present inventive concept may be applied to a variable valve lift apparatus. However, the present disclosure is not limited thereto and may be applied to a cam for reducing valve duration.

As shown in FIG. 3, a variable valve lift apparatus 1 varies valve lift and a long duration cam 10 or a short duration cam 20 selectively contacts a swing arm roller 32 of a swing arm 30 to open and close a valve 40 according to an operating state of a vehicle.

As shown in FIG. 1, with regard to the general short duration cam 20, when duration thereof is reduced, a valve lift profile, that is, a valve lift peak is reduced. Accordingly, an intake air amount is relatively small, and in particular, when the Miller cycle is embodied using the variable valve lift apparatus 1, the amount of air inflow may be insufficient.

Referring to FIG. 4( a), in the short duration cam 20 according to an exemplary embodiment of the present inventive concept, a cam lift acceleration is set unlike in the general cam.

That is, in short duration cam 20 according to an exemplary embodiment of the present inventive concept, the short duration cam 20 may be designed in such a way that a first peak P1 is formed before a center C of the cam lift acceleration, and a second peak P2 is formed after the center C of the cam lift acceleration. A relative ratio of a smaller value to a greater value of the first peak P1 and the second peak P2 may be 0.8 or more.

That is, the short duration cam 20 according to an exemplary embodiment of the present inventive concept is determined in such a way that portions of the cam lift acceleration before and after the center C of the cam lift acceleration are almost symmetrical with respect to each other.

As shown in FIG. 4( a), the cam lift acceleration of the short duration cam 20 according to an exemplary embodiment of the present inventive concept includes a steep inclination portion F and a gentle inclination portion G before the center C of the cam lift acceleration, a first peak P1, and gentle and approximately symmetrical parabola shapes H and I, and further includes a second peak P2, a gentle inclination portion J and a steep inclination portion K, which correspond to the first peak P1, the gentle inclination portion G, and the steep inclination portion F, respectively.

As shown in FIG. 2( a), since a cam lift acceleration of a general cam is designed in such a way that right and left portions of valve lift acceleration are almost symmetrical with respect to each other based on a center A of the valve lift acceleration. FIG. 2( b) shows that the cam lift acceleration has an asymmetrical shape in which an acceleration maximum value B1 on the left of a center B of the cam lift acceleration is relatively greater than maximum value B2 on the right of the center B of the cam lift acceleration. For example, a ratio of a smaller value B2 to a greater value B1 of the right and left peak values B1 and B2 based on a center B of a plot is equal to or less than about 0.7. That is, a curvature radius of a concave shape (refer to r1 of FIG. 5) of the general cam Cam1 is reduced, and thus, it is difficult to process the concave shape. Accordingly, maximum valve lift is reduced.

However, the short duration cam 20 according to an exemplary embodiment of the present inventive concept is determined in such a way that portions of the cam lift acceleration before and after the center C of the cam lift acceleration are almost symmetrical with respect to each other to achieve the valve lift acceleration plot as shown in FIG. 4( b).

FIG. 5 is a diagram illustrating a general cam and a short duration cam of a variable valve lift apparatus according to an exemplary embodiment of the present inventive concept, and FIG. 6 is a graph illustrating valve profiles of a general cam and a short duration cam of a variable valve lift apparatus according to an exemplary embodiment of the present inventive concept. Cam1 represents the general cam and Cam2 represents the short duration cam in FIG. 5.

FIG. 4( b) shows that the short duration cam 20 according to an exemplary embodiment of the present inventive concept has a minimum value Min after a center D of the valve lift acceleration plot, and thus, it is disadvantageous to degrade dynamic characteristic, but a curvature radius r2 of a concave portion of a cam in FIG. 5 may be relatively increased, thereby increasing a peak value of valve lift.

Referring to FIG. 6, when valve duration of a valve profile C1 of the general cam is reduced, a valve lift maximum value is also reduced, for example, from 8.5 mm to 6.5 mm like C2 of FIG. 6. However, in a short duration cam according to an exemplary embodiment of the present inventive concept, while reducing the valve duration, the valve lift maximum value may be relatively increased, for example, from 8.5 mm to 9 mm.

A short duration cam according to an exemplary embodiment of the present inventive concept may have a duration angle of 100 to 120 degrees between opening and closing of a valve including a ramp of the short duration cam, and even if the cam has relatively small valve duration, a maximum value of valve lift is relatively great, and thus, the cam may be applied to an engine using the Miller cycle.

In the short duration cam according to the present disclosure, a valve lift profile may be asymmetrical based on maximum valve lift of the short duration cam.

That is, referring to FIG. 6, peak positions of a valve profile of the general cam are approximate centers CP1 and CP2 of valve duration, but the short duration cam according to an exemplary embodiment of the present inventive concept is formed in such a way that a valve lift peak point CP3 is relatively retarded from the center.

When the short duration cam according to an exemplary embodiment of the present inventive concept is applied to a variable valve lift apparatus, dynamic characteristic is degraded, but a relatively high valve profile may be embodied in a relatively low speed region, and thus, fuel consumption may be enhanced using a short duration cam in a relatively low speed, for example 4000 rpm or less, and using a long duration cam with a general shape in a speed of 4000 rpm or more.

That is, the short duration cam and the variable valve lift apparatus including the same according to an exemplary embodiment of the present inventive concept, a valve lift value may be relatively increased, thereby increasing intake efficiency.

Although a short duration cam of a variable valve lift apparatus has been described, the present disclosure is not limited thereto and may be applied to a Miller cycle engine.

When the short duration cam according to an exemplary embodiment of the present inventive concept is applied to the Miller cycle, that is, a Miller cycle engine, an intake valve of which is closed before reaching the bottom dead center, although valve duration may be relatively small, an effective compression ratio may be relatively low, a knocking problem may not occur, and an effective expansion ratio may be increased, thereby increasing engine efficiency.

While this inventive concept has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the inventive concept is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 

What is claimed is:
 1. A method for manufacturing a short duration cam of a variable valve lift apparatus, the method comprising steps of: setting a cam lift acceleration of the short duration cam such that a first peak is formed before a center of the cam lift acceleration and a second peak is formed after the center of the cam lift acceleration; and setting a curvature radius of a concave portion of the short duration cam based on the set cam lift such that a relative ratio of a smaller value to a greater value of the first peak and the second peak is 0.8 or more.
 2. The method of claim 1, wherein the short duration cam has a duration angle of 100 to 120 degrees between opening and closing of a valve comprising a ramp of the short duration cam.
 3. The method of claim 1, wherein the short duration cam has a valve lift profile to be asymmetrical based on a maximum valve lift of the short duration cam.
 4. A short duration cam of a variable valve lift apparatus, wherein a cam lift acceleration of the short duration cam has a first peak formed before a center of the cam lift acceleration and a second peak formed after the center of the cam lift acceleration, and a relative ratio of a smaller value to a greater value of the first peak and the second peak is 0.8 or more.
 5. The short duration cam of claim 4, wherein the short duration cam has a duration angle of 100 to 120 degrees between opening and closing of a valve including a ramp of the short duration cam.
 6. The short duration cam of claim 4, wherein the short duration cam has a valve lift profile to be asymmetrical based on maximum valve lift of the short duration cam.
 7. A variable valve lift apparatus comprising the short duration cam of claim 4 and a long duration cam.
 8. The variable valve lift apparatus of claim 7, wherein the short duration cam is closed before reaching a bottom dead center.
 9. A method for manufacturing a cam, comprising: setting a cam lift acceleration of the cam such that a first peak is formed before a center of the cam lift acceleration and a second peak is formed after the center of the cam lift acceleration; and setting a curvature radius of a concave portion of the cam based on the set cam lift such that a relative ratio of a smaller value to a greater value of the first peak and the second peak is 0.8 or more.
 10. The design method of claim 9, wherein the cam has a duration angle of 100 to 120 degrees between opening and closing of a valve including a ramp of the cam.
 11. The design method of claim 9, wherein the cam has a valve lift profile to be asymmetrical based on maximum valve lift of the cam. 